In an optical imaging system for human detection used in security application or the like, visible light imaging and infrared light imaging are combined with each other so that the detection capability can be improved. This type of conventional imaging systems employs a simple combination of two imaging systems including a visible light imaging system and an infrared light imaging system. However, such conventional imaging systems are large in size. Additionally, complicated processes need to be performed on two optical images for data analysis. Therefore, there has been desired an imaging system capable of conducting both of visible light imaging and infrared light imaging with one camera.
In this regard, there has been proposed an image sensor that achieves visible light imaging and infrared light imaging with one chip. With this technology, images with two wavelength ranges of visible light and infrared light can be taken with one chip.
For example, the related technology is disclosed in JP-A 2006-343229 (Patent Literature 1) and JP-A 2008-204978 (Patent Literature 2).
With the technology disclosed in Patent Literatures 1 and 2, pixels for detecting visible light and pixels for detecting infrared light are independent of each other. Therefore, the resolution of an image for each of the wavelength ranges is lowered in directions in which those different types of pixels are alternately arranged. For example, when columns of pixels for detecting visible light and columns of pixels for detecting infrared light are alternately arranged, the resolution of an image becomes half in the horizontal direction. When rows of pixels for detecting visible light and rows of pixels for detecting infrared light are alternately arranged, the resolution of an image becomes half in the vertical direction. When pixels for detecting visible light and pixels for detecting infrared light are alternately arranged in the column direction and the row direction, the resolution of an image becomes 1/√{square root over (2)} in each of the horizontal and vertical directions.
Additionally, with the technology disclosed in Patent Literatures 1 and 2, points at which visible light is detected are not exactly identical to points at which infrared light is detected. Therefore, the data precision is excessively low in a field in which precise measurement is required.